Careful: Your husband may be hiding something from you. No, he isn’t canoodling with the secretary. He has been – gasp – eating salad for lunch.

Men, it appears, are dieting in secret. According to a new survey conducted by British meal-delivery service Diet Chef, nearly one in three men said they would hide dieting from friends and family. This, although 90 per cent of the men surveyed admitted wanting to lose weight. While women are increasingly comfortable debating the relative merits of olive-oil cleanses versus low-carb regimes with friends, many men still see it as embarrassing – even feminizing.

The survey found that 14 per cent of men see diets as something women do, while 29 per cent worried others would see them as vain if they found out they were concerned about their weight or appearance.

Recent diet trends have tried to counter the stigma by appearing more tough-guy-friendly. The paleo diet, popular with male bodybuilders, attempts to recreate what cavemen may have eaten before the age of agriculture – in other words, plenty of meat and eggs, some veggies and no grains.

The findings are no surprise to diet guru Harvey Brooker, who for the past 27 years has run a Toronto weight-loss clinic specifically for men. He says male dieters hide their dieting because “they don’t want to be looked at as being weak.”

Mr. Brooker has seen it all, including clients concerned that their wives will see their payments to the clinic on their credit-card statements. He runs discussion groups for male dieters to counter their tendency to diet in secret.

One client named John, a gregarious financial adviser, was so worried about what others would think about his diet program that he would deny it even when asked. “He’s lost 661/2 pounds,” Mr. Brooker says. “The first 30 pounds, he didn’t tell anybody. People would say, ‘You’re losing weight.’ He’d say, ‘I’m just cutting back.’ He wouldn’t even divulge the fact that he was coming to see us.”

Another reason men may keep mum about their weight-loss efforts is that they are afraid they will fail. “It’s the male ego entering into it,” Mr. Brooker says. “You know the old story about men: They won’t even ask for directions.”

Once they lose the pounds, however, many will announce it to family and colleagues (some of whom, no doubt, already noticed they were skipping the bacon cheeseburgers and ordering smoothies).

One of Mr. Brooker’s proudest success stories is former Ontario Progressive Conservative leader John Tory, who lost 40 pounds. He sometimes carries a medallion marking the achievement that Mr. Brooker gives to successful clients.

Mr. Brooker emphasizes that secret dieting is often far less successful – even dangerous – compared with seeking advice. “Do guys try to lose weight on their own? Continually. Are they successful? Never,” he says. “They’ll buy a book, or they’ll starve themselves, often cut the wrong things out of their intake.”